Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $182.60   13.372%   $207.0173   $207.02   $207.00   $207.00  
  Purchase #2 $32.85   11.775%   $36.7181   $36.72   $36.70   $36.70  
  Purchase #3 $112.84   7.228%   $120.9961   $121.00   $121.00   $121.00  
  Purchase #4 $194.98   13.821%   $221.9282   $221.93   $221.95   $221.90  
  Purchase #5 $197.69   12.185%   $221.7785   $221.78   $221.80   $221.80  
  Purchase #6 $60.56   12.546%   $68.1579   $68.16   $68.15   $68.20  
  Purchase #7 $38.72   5.790%   $40.9619   $40.96   $40.95   $41.00  
  7 purchase totals = $820.24       $917.5580   $917.57   $917.55   $917.60